The conventional open differential of automotive distributes driving torque evenly to its two output shafts. Various torque-vectoring designs are attempted and approached. Some of them are based on varying gear ratio as means to vary torque, as is disclosed in the patent U.S. Pat. No. 7,491,147 B2, and U.S. Pat. No. 7,708,665 B2. However such means of varying torque for particular shafts will cause the change of the rotational speed of the shafts accordingly.